/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id$
 */
package wx.xml.xalan.xpath.axes;

import java.util.ArrayList;

import wx.xml.xalan.xml.dtm.DTMIterator;
import wx.xml.xalan.xml.utils.WrappedRuntimeException;

/**
 * Pool of object of a given type to pick from to help memory usage
 *
 * @xsl.usage internal
 */
public final class IteratorPool implements java.io.Serializable {
    static final long serialVersionUID = -460927331149566998L;

    /**
     * Type of objects in this pool.
     */
    private final DTMIterator m_orig;

    /**
     * Stack of given objects this points to.
     */
    private final ArrayList m_freeStack;

    /**
     * Constructor IteratorPool
     *
     * @param original The original iterator from which all others will be cloned.
     */
    public IteratorPool(DTMIterator original) {
        m_orig = original;
        m_freeStack = new ArrayList();
    }

    /**
     * Get an instance of the given object in this pool
     *
     * @return An instance of the given object
     */
    public synchronized DTMIterator getInstanceOrThrow()
        throws CloneNotSupportedException {
        // Check if the pool is empty.
        if (m_freeStack.isEmpty()) {

            // Create a new object if so.
            return (DTMIterator) m_orig.clone();
        } else {
            // Remove object from end of free pool.
            DTMIterator result = (DTMIterator) m_freeStack.remove(m_freeStack.size() - 1);
            return result;
        }
    }

    /**
     * Get an instance of the given object in this pool
     *
     * @return An instance of the given object
     */
    public synchronized DTMIterator getInstance() {
        // Check if the pool is empty.
        if (m_freeStack.isEmpty()) {

            // Create a new object if so.
            try {
                return (DTMIterator) m_orig.clone();
            } catch (Exception ex) {
                throw new WrappedRuntimeException(ex);
            }
        } else {
            // Remove object from end of free pool.
            DTMIterator result = (DTMIterator) m_freeStack.remove(m_freeStack.size() - 1);
            return result;
        }
    }

    /**
     * Add an instance of the given object to the pool
     *
     * @param obj Object to add.
     */
    public synchronized void freeInstance(DTMIterator obj) {
        m_freeStack.add(obj);
    }
}
